Prior art pipe fittings are available which act as either compression fittings or push-fit fittings, but not both.
For example, JP 2001074178 (Bridgestone Corp), which aims to reduce the number of parts constituting a pipe joint, is a push-fit fitting but is not a compression fitting. This fitting includes a grip ring (1) which comprises a cylinder/ring made of resin, with a number of metallic claws or teeth embedded in the ring such that the tips of the teeth protrude to engage the pipe that is fitted. A cap (15) screws onto the pipe body (11) but does not act on the grip ring (1). The cap simply retains the O-ring in place and prevents it from moving under pressure, but does not compress the O-ring and therefore does not act as a compression fitting. This is clear from FIGS. 5, 6 and 7 of the patent.
CN 201237049 (PRIORITY DATE Oct. 7, 2008)
This is a utility model (registered design) for a quick pipe joint for a compressed air pipe. The pipe joint comprises a joint pipe (1) (see drawings) and a press cover (2) detachably connected to the joint pipe by means of a screw thread. A clamp ring base (5) is arranged on the head section of the joint pipe. The inner end of the clamp ring (5) protrudes into the joint pipe. A sealing ring (4) abuts against the clamp ring base (5). The inner ring of the sealing ring protrudes (stands proud) out of the inner diameter of the clamp ring base. A metal elastic clamp ring (6) is arranged at the outer end face of the clamp ring base (5) and includes a ring body and claw teeth folded in the direction of the clamp ring base. A bevel ring is arranged at the opening of the clamp ring base and the claw teeth about the bevel ring. A pusher (7) abuts the outer end of the elastic clamp ring and a boss (on the press cover 2) abuts the other end of the pusher.
In use, the press cover (2) is screwed tightly and the boss on the press cover causes the pusher to drive the elastic clamp ring (6) against the bevel ring, causing the teeth to “expand” and clamp the pipe.
Although the pusher acts against the clamp ring to expand the teeth and clamp the pipe, and therefore allows it to act as a push-fit fitting, it does not engage the O-ring at all. This is clear from FIG. 1 that the clamp ring base 5 engages and abuts against the end of the joint pipe 1 which prevents the clamp ring base acting upon the O-ring 4. Accordingly, and although the O-ring may protrude into the inner diameter of the clamp ring base, it simply acts as a seal and is not compressed about the compressed air pipe. The fitting of CN 201237049 therefore is a push-fit fitting but not a compression fitting or a push-fit compression fitting.
It is an object of this invention to provide a push-fit pipe coupling which has the additional advantage of including a nut which may be tightened thereover to provide additional gripping force and better sealing.